416 J.S. Lee—An Outline of Chinese Geology. 
Basin of Su-chuan the Jurassic rests unconformably upon the older 
rocks; while inside the Red Basin and in the Kuei-chou Basin it 
is apparently conformable with the everlying and underlying rocks. 
As previously remarked, during the transitional period from the 
Paleeozoic to the Mesozoic a widespread and far-reaching change in 
physiography and physiographical conditions seems to have induced 
a rapid evolution of fauna and flora in China as in other parts of the 
globe. The physical change in China is, however, as a rule, neither _ 
indicated by a sharp contrast in the lithological character of the rocks 
formed during the period, nor by an unconformity which extends 
over alarge area. .Subaerial denudation on the lands proceeded 
simultaneously with the continuous deposition in their neighbouring 
waters. In this way the several Permo-Mesozoic series were 
presumably formed. 
During the Lower Triassic time the Tsing-ling Range apparently 
stood well above the rest of the country. Its general trend could 
not have been very different from what it is to-day. By this range 
the shallow inland sea in the north was separated from an arm of the 
open ocean, which covered eastern Su-chuan, western Hu-peh, 
parts of Hu-nan and Kwei-chou, and eastern Yun-nan. 
On the arrival of the Muschelkalk epoch the open Triassic ocean 
with a pelagic fauna made a decisive move from the Himalaya 
region towards the north-east, and succeeded, at least, in invading 
south-western China. Theformation of the Middle Triassic Limestone 
was no doubt due to the intreduction of true marine conditions. As 
the Middle Triassic sea started to retreat towards the south-west, 
estuaries and lagoons naturally came into existence. In these 
waters were deposited the Rheetic coal-bearing series. Towards the 
end of the Rhetic epoch south-western China again started to sink, 
resulting in the formation of the Jurassic dolomite, but many parts 
of western China gradually rose above the water. The separation 
of a huge lake, the Lake of Su-chuan, from the open sea had its 
initiation in all probability at this time. 
The climate was then suitable for the growth of coal-making 
vegetation, and consequently coal seams were laid down in the lake 
during the Liassic time. Owing to occasionally excessive 
evaporation the waterin the Lake of Su-chuan became highly saline ; 
eventually seams of gypsum and rock salt were deposited. Under 
such climatic conditions, and in a water so heavily charged with 
macerated vegetable matter, it is readily imaginable that minute 
organisms multiplied themselves at an enormous rate when the 
water waslesssaline. Much of the mother substance of the petroleum 
in Su-chuan may have had its origin in this way... Many of the 
depressed areas in northern China were likewise covered by inland 
waters, in which coal-bearing rocks were deposited. The flora that 
then thrived in China was closely related to that of Siberia and 
Spitzbergen, showing that these countries were attached to one 
1 W.S. Boulton, Presidential Address to Brit. Assoc. Adv. Sci., Section C, 
Newcastle-on-Tyne, 1916, p. 12. 
